1. Field of the Invention
The present invention relates to a method of communication between a mobile station and a base station in a mobile communication system, and more particularly, to a method of communication between a mobile station and a base station in a mobile communication system of IMT-2000 communication network basis, which is suitable for effective transmission of various multimedia information within a given channel capacity.
2. Background of the Invention
In general, there are bidirectional transmission and unidirectional transmission in signal transmission between a base station and a mobile station in the mobile communication system. In the bidirectional transmission, a plurality of forward time slots and backward time slots are alternatively assigned to a communication channel established between the mobile station and the base station, for transmission of data in time slot units assigned to a same time. The time slot means a time interval of information transmission on the communication channel. In the present invention, the time slot for use in information transmission from the base station to the mobile station is called as down link slot, and the time slot for use in information transmission from the mobile station to the base station is called as an up link slot.
FIG. 1 illustrates an architecture of down link slots and up link slots of a bidirectional communication in a related art mobile communication system.
Referring to FIG. 1, data frames are transmitted in a forward or backward direction during time slots S1˜S4 assigned in advance. That is, the data frames are transmitted between the mobile station and the base station continuously alternating the down link slot S1 and S3 and the up link slots S2 and S4. That is, the data frames produced at the base station or the mobile station are transmitted repeatedly alternating assigned down link slots and up link slots. This type of signal transmission has been developed on the assumption that the mobile communication network serves for a speech data transmission in which a ratio of data transmission between a transmission side and a reception side is 1:1. Due to this reason, a trend is kept on, in which the down link slots and the up link slots are assigned simply at an equal ratio to most of current mobile communication devices. However, in a mobile communication service of IMT-2000 communication network basis, not only speech services, but also a variety of multimedia services, such as internet service and image broadcasting service are provided. In the internet or image service, an asymmetric transmission system is employed, in which an amount of data is transmitted in down link slots is relatively greater than an amount of data transmitted in up link slots, resulting to use slots of one direction of the down or up link slots continuously while slots of the other direction are almost not used in a case the multimedia service is given using a communication network having the down link slots and the up link slots assigned equally. In such a case, there is a problem that a capacity of a given channel is not used effectively. Consequently, to match to such an asymmetric transmission system, a TDD (Time Division Duplex) system is suggested, in which different numbers of down link slots and up link slots are assigned. That is, numbers of down link slots and up link slots are varied with amounts of data.
However, the TDD system has many problems in practical applications. The greatest problems are that random access and synchronization acquisition are difficult because periods of the mobile station and the base station which have regular down link slots and up link slots are not known in advance when the mobile station attempts to start an initial communication. In order to solve such problems, as shown in FIG. 2, an improved TDD system is suggested, which employs both a static period (TDD1) having down link slots and up links slots assigned therein in a regular alternation and a dynamic period (TDD2) having down link slots and up link slots irregularly assigned therein according to amount of the data to be transmitted. In the improved TDD system, the problems of random access and the synchronization acquisition between the mobile station and the base station can be easily solved by using the static period (TDD 1). And, since a communication can be made by providing numbers of down link slots and up link slots in the dynamic period (TDD2) varied with an amount of data, a given channel capacity can be used, effectively.
Thus, the static period (TDD1) in which the down link slots and the up link slots are assigned alternatively is provided for solving the problems in random access and synchronization. However, there are no suggestions on standards or techniques which improve an efficiency of given channel capacity in cases when numerous subscribers require calls or hand-off almost at a time in a city center where many offices are concentrated or a business quarter where many people gather. Therefore, there is no appropriate way to solve the problem when a number of call or hand-off required on the same time exceeds the given channel capacity. Accordingly, a technique in need, which can maximize an efficiency of a given channel source in a case when there is an excessive number of call or hand-off requirements in the IMT-2000 communication network in which the multimedia service is provided.